I'd like to understand how `ContentNegotiation` wo...

# ktor

[Tom]

I'd like to understand how ContentNegotiation works so I can understand if the behaviour I am running into is a bug, or, expected. The situation is that using Ktor Client I want to send a POST request of type application/json with an Accept image/jpeg header. The behaviour I am seeing is that using the headers {} function to set the Accept header of type image results in the Accept type being application/json. I am using kotlinx serialization as my serialization plugin. Given this client, for example:

HttpClient(Java) {
            install(Auth) {
                bearer {
                    loadTokens {
                        BearerTokens(
                            accessToken = "<redacted>",
                            refreshToken = null,
                        )
                    }
                }
            }
            install(Logging) {
                level = LogLevel.ALL
            }
            install(ContentNegotiation) {
                json()
            }

Followed by this request:

return httpClient
            .post(URL) {
                contentType(ContentType.Application.Json)
                setBody(request)
                headers {
                    append(HttpHeaders.Accept, "image/jpeg")
                }
            }.readRawBytes()

Clearly shows from the Ktor logging that the Accept header is set to `application/json`:

METHOD: POST
COMMON HEADERS
-> Accept: application/json
-> Accept-Charset: UTF-8
-> Authorization: Bearer <redacted>

Am I mis-using the configuration API?

[Aleksei Tirman [JB]]

I cannot reproduce the problem with the following code:

val client = HttpClient(Java) {
    install(ContentNegotiation) {
        json()
    }
}

val response = <http://client.post|client.post>("<https://httpbin.org/post>") {
    contentType(ContentType.Application.Json)
    setBody("test")
    headers {
        append(HttpHeaders.Accept, "image/jpeg")
    }
}

println(response.bodyAsText())

As a result, the Accept: image/jpeg,application/json header is sent to the server. Since the json method registers the content converter for the application/json content type, the Accept header contains both content types.

[Tom]

Which versions are you using?

[Aleksei Tirman [JB]]

3.1.1

[Tom]

Sort of user error? IntelliJ keeps auto importing import io.ktor.http.headers which is not the correct header builder. Even after I delete it to specify the proper import import io.ktor.client.request.headers it just keeps bringing it back until you delete the associated code. Mystery solved, but annoying! Thanks.

[Aleksei Tirman [JB]]

Ah, that's the problem. Feel free to file an issue.